The present invention relates to a semiconductor device provided with a heat-sink and a method of manufacturing the same, particularly, to a semiconductor device in which a lead-frame is fixed to a heat-sink and a method of manufacturing the same.
A semiconductor device in which a lead-frame is fixed to a heat-sink is disclosed in, for example, Japanese Utility Model Disclosure (Kokai) No. 7-10955.
In this prior art, a polyimide-based resin containing a crystalline silica having a high heat conductivity is printed on a heat-sink, followed by applying a heat treatment to the printed resin to form a polyimide-based resin layer. Then, an epoxy resin having a good adhesivity is printed on the polyimide-based resin, followed by adhering a lead-frame assembly to the heat-sink with the epoxy resin interposed therebetween. Further, the semiconductor device is sealed with a resin molding body except the tip of the outer lead by using a known transfer mold.
In this prior art, excellent heat dissipating properties can be obtained because a polyimide-based resin layer containing 30 to 60 wt % of crystalline silica having a good heat conductivity is interposed between the lead-frame assembly and the heat-sink.
In this prior art, however, the polyimide-based resin layer formed on the heat-sink is adhered to the lead-frame with an adhesive epoxy resin layer interposed therebetween. As the result, a heat dissipating efficiency is decreased by amount that the epoxy resin layer provided between the lead-frame assembly and the heat-sink.
What should also be noted is that, since an epoxy resin layer is formed on the polyimide-based resin layer, a difficulty arises if the sealed semiconductor device is used for an unexpectedly long period of time or a power semiconductor device generating a large amount of heat is sealed with the resin. Specifically, cracks tend to occur in the bonding interface between the polyimide-based resin layer and the epoxy resin layer because of the difference in thermal expansion coefficient between the two.